Relax thermal products are made from food grade SUS304 stainless steel material (18.8).Relax insists on using premium 18.8 Stainless Steel material for all its steel products.This is to ensure only high quality and long lasting products are delivered to the end user.Relax 18.8 Stainless Steel Thermal Flask keeps your drink warm/cold all day long with its double wall , the insulation keeps your favorite drink warm/cold for hours.